I actually saw a sperm plug wedged inside of my het lavender female's vent after a particularly intense session with her boyfriend last season. I assumed it was probably a good thing, since it was probably carrying some extra sperm. Plus it proved that the boy knew what he was doing. The female went on to lay five beautiful fertile eggs.
...Buuuut this is only my second season, and that was a 2007 pair. That het lavender boy was going crazy the previous winters waiting for his girlfriend to come up to size, so I think he was really out to succeed.
I might try that plug-on-the-back-of-the-female trick with my pewter and het pied pair! I'm getting tired of watching them ignore each other.